Electroacoustic transducers of the type having a laminated piezoelectric element and a vibration plate on which the laminated piezoelectric element is placed, are well-known. The laminated piezoelectric element deforms according to electrical signals, and this deformation causes the vibration plate to vibrate and the electroacoustic transducer generates audible waves.
In many cases the combined laminated piezoelectric element and vibration plate have similar shapes, such as both shaped like a circle or both shaped like a rectangle. When they have similar shapes, the laminated piezoelectric element and vibration plate can contact each other over a larger area, and consequently the sound pressures of the electroacoustic transducer can be increased.
On the other hand, the vibration plate is oftentimes circular in shape. This is because a rectangular vibration plate may give inconsistent deformation when it vibrates and the sound quality tends to drop as a result. On the other hand, a polygonal laminated piezoelectric element demonstrates excellent material yield, and is therefore more cost-effective, compared to a circular laminated piezoelectric element because piezoelectric materials are expensive. However, it is extremely rare that a polygonal laminated piezoelectric element is combined with a circular vibration plate.
FIG. 15 shows the piezoelectric acoustic component 61 described in Patent Literature 1, which is one of a few examples of prior art. The piezoelectric acoustic component 61 has a rectangular piezoelectric plate 62, and a disk-shaped metal plate 63 on which the piezoelectric plate 62 is placed. The piezoelectric acoustic component 61 fits into a ring-shaped case 64 having a concentric step on the inner periphery side, which is then embedded into a mobile phone, headphone, other mobile acoustic device, and the like.
For the piezoelectric plate 62, a laminated piezoelectric element is used. FIG. 16 shows the internal structure of the laminated piezoelectric element 65 described in Patent Literature 2. The laminated piezoelectric element 65 comprises piezoelectric layers 66 and electrode layers 67 that are stacked alternately. The electrode layers 67 include a first surface electrode layer 68 formed on the first surface of the laminated piezoelectric element 65 on the side opposite the one contacting the metal plate 63, and a second surface electrode layer 69 formed on the second surface on the side opposite the first surface (side contacting the metal plate 63). The electrode layers 67, including the first surface electrode layer 68 and second surface electrode layer 69, are connected alternately to one of a pair of connection electrodes 70 having different polarities. There are an odd number of piezoelectric layers 66, and the first surface electrode layer 68 and second surface electrode layer 69 are connected to the pair of connection electrodes 70 having different polarities, respectively. The connection electrodes 70 are formed by through holes. A lead wire 71 is soldered to the first surface electrode layer 68. The laminated piezoelectric element 65 is placed on the disk-shaped metal plate 63 with its second surface making contact, and the second surface electrode layer 69 and metal plate 63 are connected to each other electrically. Electrical signals are applied to the laminated piezoelectric element 65 via the lead wire 71 and metal plate 63. The laminated piezoelectric element 65 deforms and this deformation causes the vibration plate 63 to vibrate, and the electroacoustic transducer 61 generates audible waves.